LED-based high-mast lighting test on an airport apron reveals the need for careful design while Princeton University outdoor SSL research reveals the benefits and obstacles to controls and dimming.
The DOE has published two new Gateway reports on LED installations in outdoor settings. At the Philadelphia International Airport (PHL), the Gateway trial, including two stages of high-mast product tests on the apron, has shown that LEDs can deliver energy savings in the outdoor lighting application, but that application demands require careful design practices. On the Princeton University campus in New Jersey, the DOE studied four different solid-state lighting (SSL) projects dating back to 2008 to understand the successes that the university has had with LED technology and how the facilities staff has evolved its thinking on LED lighting over time.
Airport high-mast lighting
High mast lighting has been an outdoor application where LEDs have not pervaded as rapidly as in other street and area lighting uses. We did report on an airport high-mast installation in Munich, Germany. Moreover, some states have started to turn to LED-based high-mast lights on freeways as in the case of Maine. As LEDs get brighter, SSL products become a better fit for high-mast outdoor lighting whereas early products were too large and heavy for the application.
In the Gateway project at PHL, the airport staff began considering a transition to outdoor lighting with LEDs in 2013. The high-mast lights are critical for nighttime operations illuminating baggage, tow-truck, and fueling operations along with allowing the pilots to make accurate preflight inspections. The existing high-pressure sodium (HPS) lights utilized 1,758,450 kWh annually. LEDs were seen as a significant opportunity to save energy and to reduce maintenance that disrupts airport operations.
For simplicity, the airport replaced three HPS luminaires at one terminal with SSL products in October 2014. When the luminaires for that project were selected, the staff could find only a single product rated to produce 60,000 lm — the light level that computer simulations suggested would be needed for one-for-one replacement. The DOE visited the site and took detailed measurements on a grid before and after the SSL was installed. The LEDs did not provide acceptable light levels a long distance from the poles while delivering better performance near the poles.
The lessons learned in 2014 led to a second trial installation in May 2015 that primarily involved a change of one of the three luminaires used on each pole and a change as to how the center luminaire in each trio was aimed. The second round of tests was hampered by some failed LED modules on two of the poles. Still, the changes in aiming have been shown to solve the uniformity issues.
Based on the results of the project, the DOE reports that a transition to LED-based apron lighting could deliver 24.5% to 51.5% in savings depending on the products selected and a lighting design that might mix high- and medium-output fixtures. The LED lights were noted by a baggage handler to make it easier to read bag tags. Still, the DOE noted that diligence is required in both design and product selection. You can read the full report on the DOE SSL website.
Princeton’s first LED-based outdoor lighting installation came along a pedestrian walkway adjacent to Elm Drive and was instigated by the adoption of a Sustainability Plan adopted in 2008. Seven HPS lights were replaced with LED luminaires with the projection of 60% energy savings in the project area.
The HPS luminaires resulted in dark areas between poles and very non-uniform lighting, which had resulted in students not using the walkway at night. Even back in 2008 as LED technology was just being deployed in lighting, Princeton realized that improved beam distribution was perhaps more significant that energy savings on the project as more students began to use the walkway rather than take a longer route on campus.
The second Princeton LED project came in 2012 involving four adjacent parking lots. The project replaced 48 150W HPS lights on 20-ft poles with 68W LED luminaires and 20 100W HPS on 15-ft poles with 47W LED luminaires, for an aggregate 64% baseline savings including the HPS ballast factor.
Princeton, however, also installed occupancy and motion detectors on the luminaires with the intent to drop light levels to 20% of maximum late at night when no one was present. Princeton has only estimated the additional savings but believes that the project has delivered 80% in total energy savings.
The project was deemed a success and the university has reported better color characteristics and CRI that enable a more secure setting. The university did report that having motion sensors on each luminaire is not ideal because it leaves darker areas surrounding one pole where perhaps a person is entering a car, and that a networked system with zone control of sections of a lot might provide a safer experience.
Next up for Princeton’s outdoor lighting was a parking garage that was lit by a combination of 252 metal halide (MH) fixtures during the night and lower-power fluorescent lights that operated during the day. In 2013, the university installed 68W LED lights in place of the 200W MH lights with the SSL products set to provide lower light levels during the day, eliminating the need for the fluorescent fixtures.
Additional savings came from the combination of controls and a careful evaluation of the lighting scheme. The LEDs delivered more light than required so the SSL products were set to deliver a maximum of 90% output at installation. The staff may have to increase those levels as lumen depreciation takes hold. Motion detectors again were used to drop light levels to 20% of maximum when no one was present. And ambient light sensors limit the lighting to 50% of maximum when daylight is available.